The present invention relates to a transmission for a four-wheel drive motor vehicle, which is manually changed from two-wheel drive to four-wheel drive.
U.S. Pat. No. 4,170,273 discloses a transmission for a four-wheel drive motor vehicle having a transfer device for selecting the four-wheel drive. The transmission is a trans-axle type and has a transmission case and a transfer case attached to the rear end of the transmission case for the transfer device. An extension case is secured to the rear end of the transfer case, in which a rear drive shaft is provided. The transfer device comprises a transfer drive gear securely mounted on a rear end portion of an output shaft of the transmission and engaged with a transfer driven gear rotatably mounted on the rear drive shaft. A transfer clutch is mounted on the rear drive shaft for the engagement of the driven gear with the rear drive shaft. A front end portion of the rear drive shaft is rotatably supported by a bearing provided in a bulkhead in the transfer case. The output shaft of the transmission is supported by a bearing provided in the bulkhead, and a rear portion of the output shaft rearwardly extend from the bearing, on which the transfer drive gear is securely mounted. Namely, the output shaft is cantilevered. such a structure causes deflection of the teeth of the transfer drive gear, which will result in noise and fatigue of the gear.
Further, the construction renders the assembly and disassembly of the transmission complicated as described hereinafter. In order to assemble the transfer device, the transfer case is secured to the transmission case; thereafter the transfer drive gear is engaged with a splined portion of the output shaft and secured by a nut. On the other hand, the transfer clutch, the transfer driven gear, and a ball bearing are mounted on the rear drive shaft in the extension case. The portion of the shaft with these members is inserted into the transfer case, engaging the bearing with a hole in the bulkhead and engaging the driven gear with the drive gear. Then the extension case is secured to the transfer case. Disassembling is done in the reverse order. Such assembling that the transfer drive gear is secured to the output shaft, after the transfer case is secured to the transmission case, renders the work very complicated, causing a decrease of workability in assembly and reparing of the transmission.